During the last several weeks, a series of small earthquakes -- what seismologists call a “swarm” -- rumbled in Yellowstone. From January 17 to February 8 around 1,800 earthquakes, with a maximum magnitude of 3.8, were recorded in the Park. It is not unusual for Yellowstone to experience one or more earthquakes on a daily basis, but swarms sometimes involve more than 100 small earthquakes in a single day! So who monitors earthquakes in Yellowstone, and what do they have to say about this most recent swarm?

According to the University of Utah, which operates 26 seismograph stations throughout Yellowstone, this earthquake swarm was located about 10 miles northwest of Old Faithful, roughly half-way between Old Faithful and the town of West Yellowstone, Montana (see map here). University of Utah scientists report that of the 1,799 earthquakes recorded through 9:00 am MST on February 8, there were 14 events with a magnitude of more than 3, 136 events of magnitude 2.0 to 2.9, 1,113 events of magnitude 1.0 to 1.9, and 536 events of magnitude 0.0 to 0.9. The largest earthquake, a magnitude 3.8 event, occurred on January 20 at 11:16 pm MST. See chart showing when quakes occurred>>

Yellowstone earthquake activity is monitored around the clock by staff of the Yellowstone Volcano Observatory (YVO), a cooperative effort of the National Park Service, the U.S. Geological Survey (USGS), and the University of Utah. The YVO is one of five USGS observatories that monitor volcanoes within the United States for the purposes of science and public safety. The others are based in Alaska, Hawaii, Washington, and California.

According to University of Utah seismologists, earthquake swarms are relatively common in Yellowstone. The Park averages about 1,600 earthquakes a year, and 1,652 quakes were recorded in 2009. Yellowstone has experienced 80 earthquake swarms in the last 15 years.

This most recent swarm of earthquakes in Yellowstone prompted multiple personal reports of ground shaking from experiences inside the Park and -- for some of the larger events -- in neighboring communities in Montana and Idaho. According to YVO, the frequency of earthquakes has slowed since February 5 to fewer than ten small earthquakes per day, which is a normal level for Yellowstone.

Generally, earthquakes less than a magnitude 3.0 are not felt by people. It typically takes an earthquake of magnitude 4.0 or greater to cause structural damage, and a magnitude 6.5 earthquake to cause the surface of the ground to rupture.

What Causes Earthquakes in Yellowstone?

Yellowstone National Park is contained within the Intermountain Seismic Belt. The Intermountain Seismic Belt is a zone of earthquake activity that runs north-south from northwestern Montana, through Wyoming, Idaho, and Utah, and southern Nevada/northern Arizona. Yellowstone National Park also is an active volcano, and surface features such as its famous geysers and hot springs are direct results of the region’s underlying volcanism.

“The combination of the Intermountain Seismic Belt and Yellowstone’s active volcano creates forces that sometimes fracture the ground,” explained Dr. Hank Heasler, Yellowstone National Park Geologist. “Tectonic quakes, which are usually caused by the movement of rocks along a fault, are common in Yellowstone,” added Heasler.

While the Yellowstone Volcano is considered a "hotspot”—an area on the Earth’s surface that shows signs of long-lasting volcanic activity – there haven’t been any eruptions in a very long time. The last catastrophic eruption of the Yellowstone Volcano occurred 640,000 years ago. That eruption, which extended about 1,000 square miles, created the Yellowstone Caldera in what is now the central part of the Park. The most recent volcanic eruption of any kind in Yellowstone, a lava flow, occurred 70,000 years ago.

Yellowstone’s Earthquake History

While most earthquakes that occur in the Yellowstone area are too small to even notice without seismographic equipment, there have been some larger quakes. The most devastating earthquake on record to hit the area occurred just over 50 years ago. On August 17, 1959, the Hebgen Lake Earthquake measured 7.5 on the Richter scale. At the time, it was the third-largest earthquake recorded in the lower 48 states.

More than 80 million tons of rock crashed into a narrow canyon, blocking the Madison River and forming "Quake Lake," just outside of Yellowstone National Park. Portions of the road collapsed and ended up at the bottom of the lake. Tragically, 28 people who had been staying at a popular campground lost their lives in the event.

Upcoming Improvements in Earthquake Monitoring

More than $15 million in funds from the American Recovery and Reinvestment Act of 2009 have been allotted to help the USGS's five volcano observatories monitor volcanoes in the United States. Of these funds, $950,000 will soon make the Yellowstone Volcano the best-monitored hot spot in the world, while making online seismic information more accessible to the public than ever before.

Ten new seismic monitoring stations will be installed in Yellowstone over the next two years. In addition to the Park’s existing 26-site, seismic monitoring network, this new equipment will include sensors for river monitoring, a temperature sensor network, software tools, and display systems. It will also include a new alarm system that will allow all recorded seismic events to be posted directly to the Internet.

The GYSLC website is made possible in part by the Yellowstone Park Foundation through generous grants from Canon U.S.A., Inc. A major grant from the National Science Foundation to the Yellowstone Park Foundation funded the development of the OFVVC website.

The Yellowstone Park Foundation, a nonprofit, 501(c)3 organization, works in cooperation with the National Park Service to fund projects and programs that protect, preserve, and enhance the natural and cultural resources and the visitor experience of Yellowstone National Park.